Spray pickling processes for the surface treatment of metal



M. HYAMS SPRAY PICKLING PROCESSES FOR THE SURFACE TREATMENT OF METAL Filed Dec. 50, 1952 Jan. 2, 1962 3:; Bil-4v Ait United States Patent 3 015,588 SPRAY PICKLING PRdCESSES FOR THE SURFACE TREATMENT OF METAL Mentagu Hyams, London, England, assignor, by mesne assignments, to Amchem Products, Inc., Ambler, Pa, a corporation of Delaware Filed Dec. 30, 1952, Ser. No. 330,000 Claims priority, application Great Britain Dec. 31, 1951 1 Claim. (Cl. 13436) The invention relates to a process for cleaning the surface of metal by the chemical action on said metal at superatmospheric temperature of an aqueous acidplckhng liquid capable of dissolving metal oxide from said metal surface.

It is known to treat the surface of a metal article with an aqueous acid pickling liquid by the so-called immersion process in which process the surface undergoing treatment i wholly immersed in a bath of the treating liquid, or is partly immersed in said bath and rotated in such manner that every portion of the surface to be treated becomes immersed in the bath during the rotation.

Immersion processes are for many reasons less commercially acceptable than spray processe for the surface treatment of metal by the chemical action thereon at superatmospheric temperature of aqueous surface treatingliquid. The liquid bath in an immersion process must be large enough for the article being treated to be immersed therein in a satisfactory manner, and particularly in the case of box-shaped articles such as refrigerator cabinets and automobile bodies, the volume of liquid bath which must be provided, and maintained at superatmospheric temperature, for a load of work of given surface area is disproportionately high compared with the volume of liquid in the reservoir of an equivalent spray process of conventional design. An outstanding advantage of a spray process over an immersion process is undoubtedly a great acceleration in the rate of the chemical action of the treating solution on the surface undergoing treatment, and in many cases it only becomes possible to operate a process, or a succession of processes, in continuous manner by using spray application of the treating liquid, or by using a combination of spray application and immersion application. In the latter case, the article being treated may be rotated about a horizontal axis whilst partially immersed in a bath of the treating liquid, and at the same time sprayed with treating liquid withdrawn from the bath through a spray producing member.

Although spray processes of the type to which the invention relates are in many cases highly advantageous, the said processes as used conventionally have a number of serious disadvantages which in many cases have prevented the wider application of such processes, and in certain cases have made it impossible to use such processes on an industrial scale.

Spray treating processes of the type to which the invention relates are customarily carried out in a spray chamber, the gases entering the chamber having a relatively low temperature and low water vapor content, and the gases leaving the chamber having a somewhat higher temperature and a very substantially higher water vapor content. This increased temperature and Water vapor content of the exit gases is extracted from that portion of the treating liquid actively engaged in the cleaning process, namely the spray, with the result that the bulk of the treating solution lying idle in the reservoir from which the spray producing means is fed is at a substantially higher temperature than the relatively small portion of solution actually engaged in the cleaning process. It is an object of the present invention to provide a spray treating process of the type referred to in which the bulk of treating solution lying idle in a reservoir from which the spray producing means is fed may be at a lower temperature than the spray impinging upon the surface undergoing treatment.

The above factors have meant in practice that conventional spray processes of the type referred to have not operated with the sprays at a temperature substantially in excess of F. It is a further object of this invention to provide a spray treating process of the type referred to in which the spray may be made to impinge upon the surface undergoing treatment at a temperature substantially in excess of 170 F., and in particular at a temperature in excess of about 200 F.

According to the present invention a process of treating the surface of metal by the chemical action thereon at superatmospheric temperature of an aqueous surface cleaning liquid applied as spray from spray producing means as rapidly moving spray on to said surface comprises contacting the said spray whilst moving towards said surface with heated material the temperature of which is higher than that of the spray and is in excess of 180 F. In a preferred form of the invention, the surface cleaning liquid undergoes increase in temperature when passing as spray from the spray producing means to the surface being treated.

The process of treating the surface of metal may be a pickling process, in particular a pickling process involving the dissolution from the metal surface of metal oxide such as rust.

Since water vapor leaving the spray treating zone of a process according to the present invention is preferably derived mainly through evaporation of liquid other than that actively engaged in the treating process, it is particularly desirable, when the spray treatment is carried out in a spray chamber, to recover the latent heat present in said water vapor by extracting vapors and gases from said chamber, through compression means into heat-exchange means wherein the vapors give up substantially all their latent heat of vaporization to a heat-exchange fluid. This heat-exchange fluid may be aqueous surface treating liquid flowing on its way to the spray producing means, for example at some point between a pump and the spray producing means fed by the pump.

The vapors and gases extracted from the spray chamber through the compression means 31 may be returned by a conduit 32A to said chamber to supply heat to the spray therein by condensation upon the surface of said spray, or may be passed to a second chamber, communicating with the first chamber, in which second chamber the vapors are condensed upon spray in another process operating in accordance with the invention, and through which the metal surface undergoing treatment has passed or is about to pass.

The compression means may be a conventional axial or radial flow blower of capacity suflicient to compress and heat the vapors and gases to the degree necessary for efficient heat-exchange or condensation.

The present invention will now be illustrated by the following example.

The drawing is an outside elevation, partly exploded, of a spray cleaning apparatus utilizing my invention.

Referring to the drawing, the reservoir 21 is charged with an aqueous acidic surface cleaning solution. This solution is maintained whilst in reservoir 21 at a temperature of around 160 F. with the aid of steamheating coil 22-23, and is continuously withdrawn through pipes 24 and 25 by means of centrifugal pump 36 through the inside of the tubular heat-exchanger 26 into spray pipes 27, at a rate such that there is a complete turnover of the solution in reservoir 21 every 10 minutes. Steam at 30 p.s.i.g. is introduced through the steam spray pipes 33 so that a mixture of liquid and uncondensed steam striking the surface of an aluminium workpiece introduced at 34 and removed at 35 has an efiective temperature of 200 F. Vapors and air are continuously withdrawn from the processing chamber through pipes 28 and 29 into a Roots type blower 31 wherein they are compressed and heated to some 10 p.s.i.g. and passed through the outside of exchanger 26 countercurrent to the solution entering from pipe 25, condensed liquid and air being vented at 32 to a warm water rinse tank, not shown.

I claim:

Process of cleaning the surface of metal in a spray chamber by the chemical action on said metal at superatmospheric temperature of an aqueous acid pickling liquid capable of dissolving metal oxide from said metal surface, which comprises applying said aqueous acid pickling liquid from spray producing means as rapidly moving spray on to said surface and condensing steam having a temperature in excess of 180 F. upon said spray whilst the spray is moving towards the said surface, vapors and gases being extracted during the process from said chamber through compression means and then returned to said chamber to supply heat to said spray by condensation upon the surface of said spray.

References Cited in the file of this patent UNITED STATES PATENTS 103,371 Reynolds May 24, 1870 783,868 Jarratt Feb. 28, 1905 1,434,011 Hinckley Oct. 31, 1922 1,451,981 Heller Apr. 17, 1923 1,532,789 Vollrath Apr. 7, 1925 1,602,189 Davis Oct. 5, 1926 1,629,486 Dougherty May 24, 1927 2,023,496 Todd Dec. 10, 1935 2,065,462 Olsson Dec. 22, 1936 2,324,804 Van Gelderen July 20, 1943 2,330,655 Zucker Sept. 28, 1943 

